1. Field of the Invention
This invention relates to sealed bearing rotary cone rock bits having lubricant reservoir systems.
More particularly, this invention relates to sealed bearing rotary rock bits having lubricant reservoir systems that require protection from erosion during rotary cone rock bit boring operations.
2. Description of the Prior Art
It is well-known that rotary cone rock bits are subjected to extremely harsh conditions during earth boring operations. Each rock bit is subjected to hard formations, as well as the erosive effects of downhole hydraulics when the bits are run with drilling "mud". In addition, it is not uncommon for rotary cone rock bits to be subjected to drillstring weights of up to 40,000 pounds. Additionally, the cuttings resulting from the borehole drilling operation have an extremely abrasive quality and contribute to the erosion of the various parts of the rotary cone rock bit.
Drill bit manufacturers have therefore attempted to protect the drill bit while running in the aforementioned environment.
U.S. Pat. No. 3,130,801 utilizes a series of tungsten carbide inserts in the surface of the leg. The purpose of the inserts is to act as a reamer for the borehole to maintain the "gage" of the hole. The gage of the hole is the diameter of the hole as the bit works in an earth formation. Obviously, if the gage of the hole is allowed to become undersized, any new rock bit that follows a worn rock bit that has been removed from the hole will "pinch" as it is lowered into the hole, thereby causing premature failure of the new bit. This invention suggests using inserts near the shirttail portion of each leg of the three cone bit. The shirttail part of the leg is that portion of the leg nearest the borehole bottom and immediately adjacent the rotary cone rotatably secured to that particular leg. The invention teaches a means to maintain the gage of the borehole.
U.S. Pat. No. 3,513,728 describes yet another means to maintain the gage of a borehole. This particular patent deals with air bits; i.e., rock bits that utilize air as a means to flush detritus from the borehole bottom, as well as a means to cool and lubricate the bearings of the bit. This patent, like the foregoing '801 patent, utilizes a multiplicity of flush-type tungsten carbide inserts inserted in the shirttail portion of the leg immediately adjacent the rotary cone secured to that particular leg.
U.S. Pat. No. 4,140,189, assigned to the same assignee as the present patent application, describes a sealed bearing rotary cone rock bit and a means to maintain a gage of a borehole while the rock bit works in the earth formation. This patent utilizes a pair of tungsten carbide inserts that are interference fitted within the outside surface of each leg of the rock bit. This patent, however, differs from the two foregoing prior art patents in that each of the inserts extend well beyond the face of the leg of the rock bit. The inserts are preferably diamond-tipped tungsten carbide inserts that serve primarily to maintain the gage of the borehole.
The present invention goes beyond the state of the art in that a means is provided to protect the lubrication reservoir system in a sealed bearing rotary cone rock bit. A series of flush-type inserts are provided around the peripheral edge of the reservoir cavity or chamber to protect a cover cap for the reservoir system from becoming disengaged from the rock bit leg. The cover cap, for example, is retained within the reservoir system by a snap ring that is secured within an annular groove formed in an opening to the reservoir chamber formed by the leg of the rock bit. The unprotected leg could easily erode down to the retention snap ring groove near the opening to the reservoir, resulting in the loss of the cover cap as the rock bit works in the borehole. Obviously, loss of the cover cap means immediate loss of all lubricant for the rock bit bearings, hence early catastrophic failure of the bit occurs.